The leaf of a conifer (6)
I believe the answer is:
needle
'the leaf of a conifer' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for needle that I've seen before include "spur" , "Movable bar in a compass" , "Annoy by constant criticism" , "Annoy, tantilise" , "be irritating ?" .)